Bonding compositions which contain organic solvents and serve to bond rubber to metals or other, nonmetallic, substrates under vulcanizing conditions have been known for a long time. They usually contain polymeric film-forming substances, one or more adhesion promoting cross-linking agents, fillers, pigments and processing aids. Owing to their content of organic solvents, such bonding compositions have disadvantages from the point of view of pollution, toxic behavior and inflammability.
Other bonding compositions are known which comprise aqueous dispersions containing organic polymeric film-forming substances as well as cross-linking agents, adhesion promoters, fillers, pigments and processing aids, which are dispersed or dissolved in water.
Published German Application No. DE-OS 26 54 352 discloses a bonding composition which comprises an aqueous polymer dispersion and serves to bond natural or synthetic rubber to metallic or nonmetallic substrates under vulcanizing conditions. The known bonding composition contains organic film-forming substances such as halogen-containing or chlorosulfonated rubber, also an aromatic polynitroso compound, such as dinitrosobenzene, adhesion promoters and a coactivator. The coactivator used in the known bonding composition is an organo-functional phosphonic acid or a partial ester of phosphoric acid and may consist, for example, of vinylphosphonic acid or phosphoric acid monoaminoethylester. The contact of toxic phosphorus compounds in such bonding compositions is a disadvantage in the handling thereof.
German patent publication No. DE-AS 17 19 093 discloses a bonding composition which comprises an aqueous vinyl acetate/ethylene copolymer latex. The bonding films are improved as regards solvent resistance and mechanical properties at high temperatures by the addition of a cross-linking agent, e.g. triallylcyanurate or glycidylacrylates.
U.S. Pat. No. 4,119,587 discloses a bonding composition which in a solvent contains a halogen-containing polymer, an aromatic nitroso compound, a lead salt of phosphoric acid or of an organic dicarboxylic acid as well as a maleinimide compound,.particularly phenylene bismaleinimide. That known bonding composition also fails to avoid the disadvantages involved in the use of organic solvents, such as toxicity, inflammability and pollution.
The previously known aqueous bonding compositions have disadvantages residing in that they have no universal utility regarding the elastomers to be bonded and that they result in much lower bond strengths than solvent-containing bonding compositions.